How to add an entry to a file?

Question

linux

Good afternoon, tell me how to add an entry to a file from the terminal?
For example, such a condition
Add
192.168.1.1 after the line IPADDR=
255.255.255.0 after NETMASK=
What would the condition look for, if there is, it should add a value, if not, then + parameters and value.

Answer 1

1. > vim ./file
2. > /IPADDR (поиск) (нажать / и ввести строку, нажать enter)
3. > f= 
4. > a (insert mode) (нажать а)
5. > 192.168.1.1
6. > esc (нажать ESC)
7. > /NETMASK
8. > шаг 3 и 4
9. > 255.255.255.0
10. > esc
11. > :wq (сохранить и закрыть) (нажать : и ввести 2 буквы)

Answer 2

apt-get install mc